This application claims priority to an application entitled xe2x80x9cPower Control Apparatus and Method in a Wireless Communication System Using Scheduled Packet Data Service Channelxe2x80x9d filed in the Korean Industrial Property Office on Mar. 10, 2000 and assigned Serial No. 2000-12059, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to an apparatus and method for controlling power of a traffic channel in a wireless communication system and in particular, to an apparatus and method for controlling power of a scheduled packet traffic channel.
2. Description of the Related Art
FIG. 1 shows the structure of a conventional wireless communication network, and FIG. 2 shows a method for assigning a radio traffic channel in the conventional wireless communication network of FIG. 1.
Referring to FIGS. 1 and 2, a description will be made of a method for assigning a radio traffic channel in the conventional wireless communication network. As shown in FIG. 1, a simple method shown in FIG. 2 is conventionally used to assign a radio packet data channel to a mobile station.
To assign a radio packet data channel to a mobile station, base station controllers (BSSs, 111-11M inquire of associated base transceiver systems (BTSs) 101-10N about whether it is possible to assign a radio packet data channel to the mobile station. Upon receipt of the radio packet data channel assignment request in step 211 the BTS determines in step 213 whether there is an available radio packet data channel (e.g., a supplemental channel (SCH) in a CDMA-2000 system). In this case, the BTS also determines whether there is available power or whether there is an available code in the CDMA system. If it is possible to assign the radio packet data channel, the BTS transmits a channel assignment message to the BSC, and then-exchanges radio packet data channel assignment-related signaling messages with the mobile station, by performing steps 215-219. Otherwise, when there is no available radio packet data channel, the BTS transmits a reject message to the BSC in step 221, and the BSC then attempts to request assignment of the radio packet data channel after a lapse of predetermined time.
However, this radio traffic channel assignment method has the following disadvantages. In the following description, a xe2x80x9cradio traffic channelxe2x80x9d or a xe2x80x9cradio packet traffic channelxe2x80x9d is assumed to be a supplemental channel (SCH) for transmitting radio packet data.
First, describing channel assignment for the case where there is an available radio packet data channel, an assigned radio packet data channel cannot be used by other users beginning at a predetermined time before the base station system (BSS) exchanges data with the mobile station. That is, the radio packet data channel is previously assigned to the corresponding user beginning at the time when the BTS assigns the channel, so that the assigned traffic channel is wasted until before the traffics (or data) are actually exchanged. This considerably degrades performance of the radio packet data channel. For example, if it is assumed that it takes 300 ms to assign the radio packet data channel and the traffics are actually exchanged for about 300 ms between the mobile station and the base station system, the total time for which the radio packet data channel is assigned to the corresponding mobile station will become 600 ms. However, since the time for which the traffics are actually exchanged is 300 ms, the remaining 300 ms cannot be used by the other mobile stations, thus causing a waste of the assigned channel. As a result, the utilization efficiency of the radio traffic channel is decreased.
Second, since the radio packet data channel is assigned to a specific user on a circuit basis, unless the user releases the channel, other users cannot use the corresponding resources, even though the user is not transmitting and receiving packet data over the radio packet data channel. Therefore, low-channel efficiency problems and unfairness among the users arises.
It is, therefore, an object of the present invention to provide an apparatus and method for controlling power of a radio packet data channel in a wireless communication system.
It is further another object of the present invention to provide an apparatus and method for controlling power of a scheduled radio packet data channel in a wireless communication system.
It is yet another object of the present invention to provide an apparatus and method for controlling power of a radio packet data channel scheduled in a non-handoff state in a wireless communication system.
It is still another object of the present invention to provide an apparatus and method for controlling power of a scheduled radio packet data channel at a level of a pilot signal in a handoff state in a wireless communication system.
It is still another object of the present invention to provide an apparatus and method for controlling power of a radio packet data channel in a handoff state in a wireless communication system.
It is another object of the present invention to provide a leg selection apparatus and method for assigning a packet data channel when there exist a plurality of legs in a wireless communication system.
In accordance with one aspect of the present invention, there is provided a method for handing-off a mobile station receiving packet data over a second channel from a first base station system (BSS) to a second BSS by a base station controller (BSC) in a system in which the mobile station communicates with the first BSS and the second BSS adjacent to the first BSS through a first channel for transmitting a control message, and the mobile station communicates with the first BSS through the second channel for transmitting the packet data. In the method, the mobile station measures receiving strengths of pilot channels transmitted from the first BSS and the second BSS, and transmits the measured receiving strengths to the BSC through the first BSS and the second BSS. The first and second BSSs each calculate available transmission power allocable to the second channel and transmits the calculated available transmission power to the BSC. The BSC calculates a sum of the available transmission power and the measured receiving strength of the pilot channel from the first BSS and a sum of the available transmission power and the measured receiving strength of the pilot channel from the second BSS. The BSC transmits a handoff indication message to the second BSS, when the sum of the available transmission power and the measured receiving strength of the pilot channel from the second BSS is higher than the sum of the available transmission power and the measured receiving strength of the pilot channel from the first BSS.
In accordance with another aspect of the present invention, there is provided a method for controlling power of a second channel in a state where a BSC hands-off a mobile station receiving packet data over the second channel from a first BSS to a second BSS, in a system in which the mobile station communicates with the first BSS and the second BSS adjacent to the first BSS through a first channel for transmitting a control message, and the mobile station communicates with the first BSS through the second channel for transmitting the packet data. The method comprises detecting power control information of the first channel, transmitted from the mobile station; calculating transmission power SCH_power of the second channel by adding a sum of a predetermined power value power_offset and a power control step value pc_step to transmission power FDCH_power of the first channel, if the detected power control information of the first channel is a power-up command; calculating transmission power SCH_power of the second channel by subtracting the power control step value pc_step from the sum of the predetermined power value power_offset and previous transmission power FDCH_power of the first channel, if the detected power control information of the first channel is a power-down command; and controlling a signal on the second channel according to the calculated transmission power SCH_power.
In accordance with further another aspect of the present invention, there is provided a method for controlling power of a second channel in a state where a BSC hands-off a mobile station receiving packet data over the second channel from a first BSS to a second BSS, in a system in which the mobile station communicates with the first BSS and the second BSS adjacent to the first BSS through a first channel for transmitting a control message, and the mobile station communicates with the first BSS through the second channel for transmitting the packet data. The method comprises detecting power control information of the first and second channels. transmitted from the mobile station; calculating transmission power SHC_power of the second channel by adding a power control step value pc_step to previous transmission power SCH_power of the second channel, if the detected power control information of the second channel is a power-up command; calculating transmission power SHC_power of the second channel by subtracting the power control step value pc_step from the previous transmission power SCH_power of the second channel, if the detected power control information of the second channel is a power-down command; and controlling a signal on the second channel according to the calculated transmission power SCH_power.